Optical objective



SR N

Search R00 June 26, 1945. c. G. WYNNE 2,379,393

OPTICAL OBJECTIVE Filed July 20, 194:5 2 0 4.

R4 R5 R6 R7 R8 R9 9/90 +2770 3605 H2500 54 3 +5020 R3 RI I n venlor Patented June 26, 1945 Search R01 2,379,393 OPTICAL OBJECTIVE Charles Gorrie Wynne, Leicester, England Application July 20, 1943. Serial No. 495,499 In Great Britain March 29, 1943 6 Claims.

This invention relates to an optical objective for photographic or other purposes, corrected for spherical and chromatic aberrations, coma, astigmatism, field curvature, and distortion, and of the kind comprising two compound dispersive meniscus components with their concave air-exposed surfaces facing one another disposed between a front collective component and a pair of rear collective components, the three collective components all being simple elements. It is to be understood that the term front, as herein used. refers to the side of the objective nearer to the longer conjugate and the term rear to that nearer the shorter conjugate.

It is known in such an objective, in order to improve the corrections for sperical aberration and field curvature, to employ glasses having mean refractive index greater than 1.63 for the front element of the front compound dispersive component, for the rear element of the rear compound dispersive component and for the front member of the pair of rear collective components. In such known objective the two rear collective components have their shallower surfaces facing the front and the power of the collective rear component lies between 40% and 70% of the equivalent power of the whole objective.

The present invention has for its object still further to improve the correction of the aberrations of such objective, and to this end according to the invention the rear element of the rear compound dispersive component and the front member of the pair of rear collective components are each made of material having mean refractive index between 1.70 and 1.80 and Abb number between 40 and 50. As in the known objective, it is preferable for the two collective rear components to have their shallower surfaces facing the front and for the power of the rear component to lie between 40% and 70% of the equivalent power of the whole objective.

The radii of curvature of the rear surfaces of the two rear components are preferably both numerically less than 4.0 and greater than 1.5 times the equivalent focal length of the objective. The sum of the numerical values of the radii of curvature of the concave air exposed surfaces of the two compound dispersive components preferably lies between .5 and .7 times the equivalent focal length of the objective. Y

A preferred practical example of objective according to the invention is illustrated in the accompanying drawing, and numerical data for such example are given in the following table, in which R1 R2 represent the radii of curvature of the individual surfaces counting from the front, the positive sign indicating that the surface is convex to the front and the negative sign that it is concave thereto, D1 D2 represent the axial thicknesses of the individual elements, and S1 S2 represent the axial air separations between the various components. The tables also give the means refractive indices no for the D-line and the Abb 1! numbers of the materials used for the ele- In this example it will be noticed that the two rear components both have their front surfaces R9 and R11 shallower than their rear surfaces R10 and R12, and the radii of such rear surfaces lie between 1.5 and 4.0 times the equivalent focal length of the objective. The power of the rear component is about 43% the equivalent power of the whole objective. The mean refractive index of the material used for the front element of the front compound dispersive component is greater than 1.63. The numerical sum of the radii R5 and Rs amounts to about .65 times the equivalent focal length of the objective. The

' back. focal length is .5655 times the equivalent ond and third are compound dispersive meniscus components disposed with their concave air-exposed surfaces facing one another, and the first, fourth and fifth are simple collective components, the fourth component and the rear element of the third component are each made of material having mean refractive index between 1.70 and 1.80

and Abb v number between 40 and 50, in which the power of the collective rear component lies between 40% and 70% of the equivalent power of the objective the two collective rear components having their shallower surfaces facing the front.

2. An optical objective, corrected for spherical and chromatic aberrations, coma, astigmatism, field curvature and distortion, and comprising five components in axial alignment, of which the second and third are compound dispersive meniscus components disposed with their concave air-exposed surfaces facing one another, and the first, fourth and fifth are simple collective components, the fourth component and the rear element of the third compenent are each made of material having mean refractive index between 1.70 and 1.80 and Abb 11 number between 40 and 50, in which the radius of curvature of the rear surface of each of the two rear collective components is numerically less than 4.0 and greater than 1.5 times the equivalent focal length of the objective, and numerically less than that of the front surface of the same component.

3. An optical objective, corrected for spherical and chromatic aberrations, coma, astigmatism, field curvature and distortion, and comprising five components in axial alignment, of which the second and third are compound dispersive meniscus components disposed with their concave airexposed surfaces facing one another, and the first, fourth and fifth are simple collective components, the fourth component and the rear element of the third component are each made of material having mean refractive index between 1.70 and 1.80 and Abb 11 number between 40 and 50, the numerical sum of the radii of curvature of the concave air-exposed surfaces of the two compound dispersive components lying between .5 and .7 times the equivalent focal length of the objective, the two collective rear components having their shallower surfaces facing the front.

4. An optical objective, corrected for spherical and chromatic aberrations, coma, astigmatism, field curvature and distortion, and comprising five components in axial alignment, of which the second and third are compound dispersive meniscus components disposed with their concave airexposed surfaces facing one another, and the first, fourth and fifth are simple collective components, the fourth component and the rear element of the third component are each made of material having mean refractive index between 1.70 and 1.80 and Abb 11 number between 40 and 50, the numerical sum of the radii of curvature of the concave air-exposed surfaces of the two compound dispersive components lies between .5 and .7 times the equivalent focal length of the objective the power of the collective rear component lying between 40% and of the equivalent power of the objective.

5. An optical objective, corrected for spherical and chromatic aberrations, coma, astigmatism,

field curvature and distortion, and comprising five components in axial alignment, of which the second and third are compound dispersive meniscus components disposed with their concave airexposed surfaces facing one another, and the first, fourth and fifth are simple collective components, the fourth component and the rear element of the third component are each made of material having mean refractive index between 1.70 and 1.80 and Abb 11 number between 40 and 50, the numerical sum of the radii of curvature of the concave air-exposed surfaces of the two compound dispersive components lies between .5 and .7 times the equivalent focal length of the objective whilst the radius of curvature of the rear surface of each of the two rear collective components is numerically less than 4.0 and greater than 1.5 times the equivalent focal length of the objective, and numerically less than that of the front surface of the same component.

6. An optical objective having numerical data substantially as set forth in the following table:

Equivalent focal length Relative aperture Thickness Refractive Abb v Radius or air separation index no number D, 1075 1. 6135 59. 3 Rz-I-G. 101

S2 1985 lit-.3605

D 149 1. 7445 45. 8 Rs. 5443 S3 .002 Ra+5.012

Dr .057 1.7445 45.8 Rio-2. 228

S4 .002 Eli-1'3. 567

D1 .049 1.6135 59.3 Rfl- 2, 391

in which R1 R2 represent the radii of curvature of the individual surfaces counting from the front, the positive sign indicating that the surface is convex to the front and the negative sign that it is concave thereto, D1 D2 represent the axial thicknesses of the individual elements, and S1 S2 represent the axial air separations between the various components.

CHARLES GORRIE WYNNE. 

